Our transcription: It is in this fissured valley that the most frequent volcanic action occurs on the ocean floor in the form of undersea lava flows. This volcanic activity is the key to a phenomenon that long puzzled geologists. There is a great disparity between the age of the continental crust and that of the oceanic crust. The rock underlying the continents is as much as four billion years old, and yet the oldest rock found beneath the ocean dates back only about 200 million years.